I have luck. I can tell if the heater is good or not looking at it. You know when you see those dodgy heaters that have a bad design and look ugly? Those have been the ones that my LFS have told that have failed the most. Weird eh?
i use penn plax 300 watt heater. its glass, never had a problem temperature is dead on in my 75.i like the way the mouts are positionable along the heater as well